Diffuser (thermodynamics)

About: Diffuser (thermodynamics) is a research topic. Over the lifetime, 6731 publications have been published within this topic receiving 54738 citations.

PIV Measurements of Flow in a Centrifugal Blood Pump: Steady Flow

Abstract: Magnetically suspended left ventricular assist devices have only one moving part, the impeller. The impeller has absolutely no contact with any of the fixed parts, thus greatly reducing the regions of stagnant or high shear stress that surround a mechanical or fluid bearing. Measurements of the mean flow patterns as well as viscous and turbulent stresses were made in a shaft-driven prototype of a magnetically suspended centrifugal blood pump at several constant flow rates (3-9 L/min) using particle image velocimetry (PIV). The chosen range of flow rates is representative of the range over which the pump may operate while implanted. Measurements on a three-dimensional measurement grid within several regions of the pump, including the inlet, blade passage, exit volute, and diffuser are reported. The measurements are used to identify regions of potential blood damage due to high shear stress and/or stagnation of the blood, both of which have been associated with blood damage within artificial heart valves and diaphragm-type pumps. Levels of turbulence intensity and Reynolds stresses that are comparable to those in artificial heart valves are reported. At the design flow rate (6 L/min), the flow is generally well behaved (no recirculation or stagnant flow) and stress levels are below levels that would be expected to contribute to hemolysis or thrombosis. The flow at both high (9 L/min) and low (3 L/min) flow rates introduces anomalies into the flow, such as recirculation, stagnation, and high stress regions. Levels of viscous and Reynolds shear stresses everywhere within the pump are below reported threshold values for damage to red cells over the entire range of flow rates investigated; however, at both high and low flow rate conditions, the flow field may promote activation of the clotting cascade due to regions of elevated shear stress adjacent to separated or stagnant flow.

An Experimental Study on the Fluid Forces Induced by Rotor-Stator Interaction in a Centrifugal Pump

Abstract: The pressure fluctuations and the radial fluid forces acting on the impeller, the pressures in the volute, as well as the vibration of the shaft in a centrifugal pump were measured simultaneously, and their relationship was investigated. Experiments were done for various diffuser vanes, flow rates, and rotating speeds. It was demonstrated that both the blade-pressure fluctuations and the volute static pressures are nonuniform circumferentially (not axisymmetrical) under off-design operating conditions and that the two have a strong relationship. At high flow rates, the blade pressure fluctuations, induced by rotor-stator interactions, are large in areas where the volute static pressure is low. The traveling directions of the rotating pressure waves, the whirling directions of the radial fluid forces, and the most predominant frequency components of both the fluctuations and the forces are discussed, and an equation for predicting them is introduced. It was also noted that large alternating fluid forces are not necessarily associated with large pressure fluctuations. Furthermore, when measuring the radial fluid forces in the rotating frame, other frequency components, in addition to those related to the products of the diffuser vane number and the rotating frequency, may occur due to the circumferential unevenness of the pressure fluctuations on the impeller. These components are predictable.

Design optimization of an axial blood pump with computational fluid dynamics.

Abstract: A fully implantable, axial flow blood pump has been developed in our hospital. Both in vitro and in vivo tests showed that the hemolysis and thrombus characteristics of the pump were in an acceptable but not in an ideal range. Computational fluid dynamics (CFD) and in vitro test results showed that the pump worked at off-design point with a low hydraulic efficiency; CFD analysis also showed regions of reverse flow in the diffuser, which not only decreases the pump's hydrodynamic efficiency, but also increases its overall potential for blood trauma and thrombosis. To make a blood pump atraumatic and nonthrombogenic, several methods were taken to reach a final model of the optimized blood pump using CFD, which decreased the rotational speed from 9,000 to 8,000 rpm, and the design flow rate from 11 to 6 L/min. More significantly, the flow separation and recirculation in the diffuser region were eliminated, which mitigated the traumatic and thrombus effect on blood. The acceptable results of the numerical simulations encourage additional in vitro and in vivo studies.

Electrostatic spray apparatus

Abstract: An improved electrostatic spray gun for the deposition of powdered coating material on a workpiece is disclosed. The spray gun includes a housing having a barrel to which a nozzle is attached for directing the powdered material to the workpiece. A charging electrode, which is connected to a high voltage power supply, is mounted on a diffuser assembly which is clamped between the nozzle and the housing, on which the nozzle is threaded. A regulated gas flow supplied through the housing and the diffuser assembly provides a gas shield around the charging electrode to prevent a buildup of the coating material on the electrode. A novel pneumatic safety interlock continuously monitors the pressure of the gas supplied to the diffuser assembly. The interlock turns off the high voltage power supply and a pump for the coating material in response to a drop in such pressure resulting from a loose nozzle.